persistent species assemblage structure along a Hawaiian stream from catchment-to-sea

In Limahuli Stream on the Hawaiian island of Kauai, species assemblage structure was monitored from catchment-to-sea over a 6-year period to determine how individual species utilized the stream continuum spatiotemporally. A persistent pattern was identified in which ten fish and macroinvertebrate species (nine native and one alien) were distributed into distinct zones of highest abundances with overlapping species ranges. Species diversity, as quantified by a dominance measure (Berger-Parker Index), was highest and least variable at the midpoint of the continuum where upstream-downstream species' ranges converged. Reciprocal fluctuations in the population abundances of dominant species limited overall variation in species diversity to a 22% range which was interpreted as evidence of spatiotemporal persistence of the species assemblage structure. The pattern was captured in a testable, conceptual model which partitions an idealized Hawaiian stream from catchment-to-sea into five functional zones (Estuarine, Lower-Middle-Upper Reach, and Headwaters) positioned as percentages of continuum length. This model may be overlaid upon other Hawaiian streams for testing its applicability as well as to ask a variety of ecological questions about the manner in which species partition habitat spatiotemporally along biophysical gradients.